258 ANIMAL FORCES. [ii 



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ligature or section, it is transmitted to all the terminal fibrils, 

 and nerve-actions are excited in all the organs supplied with 

 twigs given off from the trunk below the point of injury, provided 

 there be no impediment to the course of the impression (359). 

 These are principles well known to physiologists (Haller^s 

 'Physiology/ §§367, 403). 



494, i. Non-conceptional internal impressions excite nerve- 

 actions only, when duly transmitted from the point of irritation 

 to the mechanical machines (493). Consequently, the brain 

 may be destroyed, or even the head wholly separated from the 

 body, and yet an internal impression made on the spinal cord, 

 or the trunk of a nerve, will develop nerve-actions in those 

 mechanical machines which receive their nerves from the cord, 

 or from the nervous trunk from below the point of irritation, 

 provided there be no impediment to its transmission downwards 

 (483) . Thus, a frog, although headless, will leap forward, when 

 its spinal cord is irritated with a needle, so that the brain and 

 the conceptive force are as little necessary to the nerve-actions 

 of internal impressions as of external, with the condition, how- 

 ever, that the vital spirits be present in the nerves as stated 

 in § 416. 



ii. Nevertheless, there are cases in which the existence of the 

 brain and its uninterrupted connection with the limb are neces- 

 sary to the nerve-actions of internal impressions, although the 

 cerebral forces and the mind do not come into action. In the 

 natural condition of the animal, certain functions are per- 

 formed by both kinds of vis nervosa acting at the same time, so 

 that ordinarily they are both direct nerve- actions of external 

 impressions and nerve-actions of non-conceptional internal 

 impressions. The heart, diaphragm, and muscular system 

 generally, will be subsequently referred to, as exhibiting ex- 

 amples (575, 524, 514). In instances of this kind, a shock 

 may easily injure, enfeeble, or interrupt the functions so com- 

 pounded, by causing one of the two kinds of vis nervosa to cease 

 to operate ; although the other is able of itself to restore the 

 disturbed functions, when after this interruption its influence 

 on the mechanical machines be renewed. Consequently, if 

 the trunk of a nerve distributed to a mechanical machine, the 

 natural function of which is at the same time both a direct 

 nerve-action of an internal impression and a nerve-action of an 



